1. Field of the Invention
The present invention relates to a fuel injection control apparatus and method for an internal combustion engine which is supplied with a fuel by an in-cylinder fuel injection valve for injecting the fuel into a cylinder, and a port fuel injection valve for injecting the fuel into an intake system including an intake port.
2. Description of the Prior Art
Conventionally, as this type of fuel injection control apparatus for an internal combustion engine, one described, for example, in Laid-open Japanese Patent Application No. 2005-337102 is known. In this fuel injection control apparatus, the proportion of an in-cylinder injection amount injected from an in-cylinder fuel injection valve to a port injection amount injected from a port fuel injection valve is set in accordance with a detected operating condition of an internal combustion engine. Also, when the proportion of the port injection amount decreases while the proportion of the port injection amount increases, an increased amount of the port injection amount is divided into a primary injection for injecting an amount of fuel in accordance with the operating condition of the internal combustion engine, and a secondary injection which precedes the primary injection. Also, the amount of fuel injected in the secondary injection is set to the amount of fuel sticking to the inner wall of an intake passage, thereby compensating for a lack of fuel supplied to a combustion chamber due to the fuel sticking to the inner wall of the intake passage.
When a port fuel injection valve is provided in conjunction with an in-cylinder fuel injection valve, as is the case with the foregoing conventional internal combustion engine, the sticking of fuel is not limited to a fuel injected from the port fuel injection valve, but is involved in a fuel injected from the in-cylinder fuel injection valve, where the fuel can stick to the inner wall surface of a combustion chamber, for example, the inner wall surface of a cylinder, the top surface of a piston, and the like. However, in the conventional fuel injection control apparatus, a correction against the sticking is made only for a fuel injected from the port fuel injection valve, so that a fuel transport behavior of the whole cylinder, including the sticking of a fuel injected from the in-cylinder fuel injection valve, is not reflected. As a result, the amount of fuel actually used in the combustion in the combustion chamber cannot be appropriately controlled, failing to achieve a desired air-fuel ratio.
Also, in this fuel injection control apparatus, the correction against the sticking is performed exclusively in an operating condition in which the proportion of the port injection amount is increasing, so that an appropriate fuel injection amount reflecting a fuel transport behavior cannot be set in other operating conditions of the internal combustion engine. Further, since fuel injection amounts are set by control approaches different from each other between the operating condition in which the proportion of the port injection amount is increasing and other operating conditions, the entire control logic is complicated, and the air-fuel ratio is more likely to vary before and after switching between the control approaches.